The Claus process is a gas desulfurizing process for recovering elemental sulfur from gaseous hydrogen sulfide. It was first developed in the 1880's and has become an industry standard for refineries, chemical plants and natural gas processing plants. As petroleum and natural gas is tending to contain ever increasing amounts of sulfur compounds while fuel regulations are tending to mandate less allowable sulfur in fuel, Claus processes become increasingly important.
A Claus plant, which is a multi-step process within a larger industrial plant is arranged to recover sulfur from gaseous hydrogen sulfide. Typically, elemental sulfur is produced by a thermal step and several catalytic steps. Elemental sulfur is separated from the Claus plant as a liquid at one or more condensers.
While current sulfur condensers have proven satisfactory for condensing sulfur, there is a need for improvement in the quality of the sulfur condensed. The problem is that the condensed sulfur includes dissolved H2S. Over an extended time, the H2S will eventually disassociate from the liquid sulfur and accumulate as a toxic and flammable gas in vapor spaces at the top of the storage or transport vessels. Since an unsafe condition is possible until the sulfur is fully degassed of dissolved H2S, precautionary steps are required prior to opening a sulfur vessel and while transferring liquid sulfur from one vessel to another.
It has been found that it is the nature of a liquid sulfur produced in a sulfur condenser process that reactant hydrogen sulfide (H2S) is incorporated into the sulfur as simple dissolved H2S and also as chemically bound with sulfur in the form what is sometimes called a sulfane or polysulfane. Sulfane is H2Sx, (with x>1). H2Sx will convert back to H2S and elemental sulfur in time through an equilibrium reaction which may be accelerated with a catalyst. This is a known problem and most efforts to remove H2S from the elemental sulfur include bubbling various gases such as air and preferably inert gases such as nitrogen and carbon dioxide through the liquid sulfur while in a catalyst bed. This degassing process, while necessary, takes time and adds to the expense of capturing sulfur from refineries, gas plants and chemical plants that deal with sulfur.
Thorough degassing is imperative as capturing and disposing of H2S that is emanating from liquid sulfur storage is another issue. If the elemental sulfur is not adequately degassed, H2S emanating from liquid sulfur storage may become a fugitive emission in an area that is closely monitored for environmental compliance. In some instances, up to half of the reported emissions from a Claus sulfur recovery plant and Claus Tail Gas Cleanup unit can come from H2S emanating from liquid sulfur in storage. Without degassing operations or adequate capture and disposal technology, these additional emissions may limit the sulfur processing capability of the Claus/TGU (Tail Gas Unit) unit.
Technology is needed to reduce costs and overcome and resolve these problems without creating new disadvantages.